Learning how to create trim sheets is essential for optimisation, as you are able to reuse them across multiple assets in your scene which would otherwise require their own textures. More textures means more memory overhead, so the aim is to minimise them where possible.

Links for Brushes:

https://www.artstation.com/marketplace/p/jM7g/zbrush-stone-and-rock-damage-brushes

https://www.artstation.com/marketplace/p/zwK3N/12-hq-rock-brushes-for-zbrush-free

https://www.artstation.com/marketplace/p/3oJv/modular-rock-sculpting-free-tutorial-resources